The invention especially relates to a pressure-sensitive adhesive which is suitable for adhering front materials or backing to substrates containing plasticized polyvinyl chloride. Such vinyl substrates are used on a large scale for indoor surfaces such as wall coverings and outdoor surfaces such as vinyl-coated canvas for trucks. These vinyl substrates contain as much as 25-75 parts of monomeric plasticizer per 100 parts of vinyl resin. Letters, figures or drawings can be applied to such vinyl substrates by painting or printing with silk-screen ink. For this purpose a pressure-sensitive film imprinted with letters, figures, etc., or cut into the shape of letters, figures, etc. can also be used too.
The front layer as well as the adhesive layer of such a pressure-sensitive adhesive film must meet certain requirements in order to prevent problems occurring by migration of plasticizer out of the substrate and into the pressure-sensitive adhesive layer. If materials are used which are unsuitable for the front layer and/or the adhesive layer, the front layer may tend to wrinkle or become sticky and the adhesive layer may lose its adhesive strength.
European Patent Application 103.407 incorporated herein by reference discloses a pressure-sensitive film that is suitable for adhesion to a vinyl substrate containing monomeric plasticizer. This film comprises a first layer of polyvinyl chloride, a second layer of a plasticizer resistant pressure-sensitive adhesive, and a third layer between the first and second layers, serving as a barrier for plasticizer from the substrate. As suitable adhesives polyacrylates are disclosed that are a combination of the following monomers:
a) acrylic acid, methacrylic acid, acrylic amide and/or methacrylic amide,
b) an alkyl acrylate and/or alkyl methacrylate and
c) at least one additional ethylenically unsaturated monomer.
In European Patent Application 330,272 incorporated herein by reference the suggestion is made to replace the polyvinyl chloride outer layer and the barrier layer of the above-mentioned film by one single layer consisting of a mixture of polyvinyl chloride and chlorinated polyethylene. For the adhesive layer reference is made to the above European Patent Application.
The group of adhesives from which a choice can be made as to the adhesion of front materials that are generally based on plasticized polyvinyl chloride to substrates containing monomeric plasticized polyvinyl chloride, is therefore rather limited.
It is one object of this invention to provide an adhesive for the application stated above, offering a stronger adhesion than the adhesives know so far.
A further object of this invention to provide an adhesive that adheres strongly shortly after application to the substrate. Another object is to provide an adhesive that presents good properties when applied outside at usual ambient temperature conditions.